Corrosion resisting iron



Patented June 21, 1938 CORROSION RESISTING IRON Earle C. Smith, Cleveland Heights, and George T. Motok, Canton, Ohio, assignors to Republic Steel Corporation, Cleveland, Ohio, at corporation of New Jersey No Drawing.

Claims.

I'his invention relates to corrosion .resisting compositions and more particularly to irons or steels with new and improved properties. I

Irons and steels may be roughly divided into 5 two classes on the basis of their resistance to corrosion. The first class includes those compositions which are highly resistant to corrosion, either because of ,the absence of impurities which cause corrosion or because of the presence of added elements which make them highly resistant to corrosion. An example of this class is stainless steel. The second class includes compositions which are only mildly resistant to corrosion', due to the presence of impurities, but which possess relatively long life under corroding influences by reason of a more or less uniform dispersion of the impurities in finely divided par-' ticles. Thus, while the metal corrodes, it does so slowly and uniformly as compared with the same metal in which the impurities are. present in segregated form and where the corrosion is localized with the formation of pits or holes which soon make the article of little or no value. An example of this class in the iron of the Charls Patent No. 1,355,589.

The present inventionis based .on the discovery that nitrogen and phosphorus when present in the proper form and amounts, improve the properties of compositions of the second class, i. e., corrosion resisting irons or steels. We have found that, contrary to generally accepted belief, nitrogen in proper form and amount is not an element to be avoided, but in fact can be used to confer desirable characteristics on corrosion resisting silicon, are also similarly dispersed. Nickel may also be present in small amounts. We have found that when suchan iron contains between about 0.005% and about 0.2% of nitrogen, preferably 4 5 111- the form of more or less stable metallic nitrides, the resistance of the iron to corrosion is considerably increased and its life under mildly cor -odin'g influences is correspondingly prolonged. We believe that these characteristics. are traceirons having the fundamental composition of besmall amounts, such as manganese, sulfur and able to the existence of nitrides of iron, and

Application January 6, 1937, Serial No. 119,264

possibly of other metals which are in the steel, in the form of minute, more or less uniformly distributed needles or particles which in themselves are highly resistant to corrosion and which serve as anchors to which may adhere iron oxide which 5 forms during corrosion. These nitrides form a film which may be retained as a. protective coating over the surface portions of the iron which are less resistant to corrosion. Such a film protects the iron from continued contact with the 10 corroding agent and hence improves the resistance and prolongs the life of the iron.

We have also. discovered that, contrary to previous generally accepted beliefs, phosphorus in proper amount is not an element to be avoided 15 but in fact' can be used to advantage to confer desirablecharacteristics on corrosion resisting irons of the foregoing fundamental composition 3 and preferably containing about 0.005% and about 0.2% of nitrogen. The phosphorus should 20 be present in amounts between about 0.04% and about 0.5%. We believe that these new properties are traceable to the formation of a film on the surface of the iron during corrosive action Apparently themhosphorus is converted. into a 25 film-forming compound, which may include phosphates or phosphides when the iron is exposed to ordinary corroding influences. a

The useof phosphorus, within the range specified, is particularly advantageous when the iron 30 contains nitrogen within the foregoing range, for the nitrogen apparently exerts a dispersing effect on the phosphorus and causes it to be "more uniformly distributed thruout the iron.

-In practicing the present invention an iron or steel is made in the ordinary manner, as in an electric furnace orin an acid or basic open hearth or in a Bessemer furnaceand/or converter, and contains between about 0.15% and about 1.5% of copper and between about 0.01% and about 40 0.10% of carbon, with or without between about 0.05% and about 0.55% of molybdenum and with 'or without between about 0.01% and about 0.50% manganese. Such iron or steel will ordinarily contain up to about 0.065% of phosphonitrogen may be added when the phosphorus is added and both or either may be added to the molten metal in the furnace, in the ladle or in the molds. A

, Nitrogen carrying materials which have been found to be suitable for this purpose include nitrogen-bearing metallic materials, such as nitrides of copper or iron and cyanides of the alkali metals and alkaline earth metals. Urea or other organic compounds containing nitrogen may bev used. The alkali and alkaline earth cyanides are quite useful. For example, calcium cyanamid is satisfactory both because of its nature and its low cost, and also because the residue remaining after it has decomposed and liberated nitrogen is beneficial to the iron. Such residues are inert under corroding conditions and hence may serve as an anchorage for films of iron oxide which protect underlying portions or the iron from corroding substances. The addition of about lbs. of calcium cyanamid per ton of iron will carry a sumcient amount of nitrogen into the iron for the present purposes.

In order toinsure retention in the iron of the desired amount of nitrogen,it is preferable to have ingredients present in the iron which will act as nitrogen fixers, i. e., elements which will readily combine with nitrogen liberated in'the iron and form stable nitrides. Several metals have been found to be effective for this purpose, including titanium, vanadium, zirconium, columbium and tantalum. Silicon, aluminum, boron and beryllium are also ,good nitrogen fixers. Small amounts oi. one or more of these elements may be'used in amounts sufllcient to retain in the iron nitrogen within the limits of I defined in what is claimed.

mm about 0.005% and about 0.2%.

Having thus described the invention so that those skilled in the art may practice the same, what we desire to secure by Letters Patent is What is claimed is:-- 1 1. An iron. article to be exposed'during use to corroding conditions containing between about .01% and .10% carbon, between about .05% and about .35% and about .65% of copper, impurities and molybdenum aggregating between about 30% and about .90%, the molybdenum ranging between about .05% and about 55% the re-' mainder being iron.

3. Aniron article to be exposed during use to corroding conditions containing between about .01% and about .1% of carbon, between about 007% .and about .10% of nitrogen, between about .04% and about .5% of phosphorus, between about .35% and about .65% of. copper, impurities and molybdenum aggregating between about 25% and about .35%, the molybdenum ranging between about .05% and about .15%, the remainder being iron.

4. An iron article to be exposed during use to corroding conditions containing between about .01% and about .1% of carbon, about .10% of nitrogen, about .5% of phosphorus, about 115%- of copper, about .10% of molybdenum, the remainder consisting of iron containing small amounts of impurities.

5. An iron article to be exposed during use to corrodingconditlons composed of a low carbon,

basic, open hearth iron containing between about .005% and about.2% oi nitrogen, between about .0 4% and about .5% of phosphorus, between about .35% and about .65% copper, between about .3% and about .9% of ordinary impurities and molybdenum the molybdenum varying between about .05% and about .55%, the remainder being iron.

EARLE -C. SMITH. GEORGE T. MOTOK. 

